Charged particle microscopes typically use electrons or metal ions. Both types of microscopes are moderately reliable, and the electron microscope provides very high resolution. However, helium ion microscopes have certain advantages over the electron microscope. Light ions significantly reduce the optical diffraction effects that electrons cause and they have a smaller interaction volume when focused onto the surface of a sample by a lens. Helium ions can also provide better chemical contrast than electrons. Furthermore, the Helium ion sources can be built smaller than electron sources, providing a smaller final spot size for a given optical condition. Typically, the coherence, or energy spread, of this type of ion source is better than electron sources minimizing chromatic aberration effects that cause resolution reduction. However, prior efforts to utilize ion sources for imaging applications haven proven to be unstable and unreliable.
There is a need for a reliable and bright ion source. Such a source incorporated into an ion electro-optical system will provide very high resolution pictures having near atom resolution.